Uranium and V isotope variations in Archean sediments

In this project we investigate redox-related variations of uranium and vanadium isotopes in Archean sediments. Both V and U are mobile and well soluble under oxic conditions and become reactive and immobile under reducing conditions. Thus, traces of oxygen in the overall anoxic world of the Archean may have resulted in the mobilization of these elements and their authigenic enrichment in sediments. Uranium shows strong isotope fractionation, in particular during U reduction. Analyses of V isotope variations (51V/50V) is very challenging and became only recently possible with sufficiently high precision due to progress in instrumental analytics. The isotope fractionation behavior of V is yet largely unknown. However, recent analyses of V isotopes of Cambrian black shales (performed by our group) revealed significant isotopic variations, correlating with those of U isotopes which is promising for using combined V and U isotopes as a paleo-redox proxies. Recent findings for U isotopes indicated that microbial-mediated U reduction may provide distinct isotopic signatures. We thus expect our U and V isotope investigations on Archean black shales, and other sediment archives, to provide new information on the redox evolution of the early Earth's oceans and atmosphere and potentially on the early evolution of life.